A bandana worn in the left rear pocket of the pants. These are usually worn by gangstas, rappers, and people who are influenced by rap music. I've only seen blue and white flags, although I'm sure there's red flags too (maybe even other colors as well). The
white flag can be seen in Eminem's music
video, 'Just Lose it', and the blue flag can be seen in Snoop Dogg's music video, 'Drop it Like it's Hot'. Snoop Dogg says that his blue flag signifies that he is a crip, so it seems reasonable that a blood would wear a red one. If anyone wants to correct me, then feel free to do so.
Skaters can also be seen wearing flags. They usually wear black or white ones (although the color probably doesn't matter for them), and theirs is neatly folded into a triangular shape and only about four inches of it stick out, whereas
the gangsta/rapper/rap-influenced person
practically lets the whole thing hang out.